Abstracts

Introduction: Elocta ® is an Fc Fusion Protein classified as an extended half-life (EHL) drug for the management of patients with Haemophilia A. Several different laboratory assay methods can be used to monitor Elocta in patient plasma samples.Methods: In a supplementary UK NEQAS BC exercise 4 lyophilised samples containing Elocta were distributed to 81 participating centres.Sample S19:02 was from a patient with severe Haemophilia A treated with Elocta, but prior to sample collection was at a treatment trough level.S19:03 was from a patient with severe Haemophilia A patient, treated with 2000 iu/kg Elocta 15 minutes prior to sample collection.Samples S19:04 and S19.05 were constructed by 'spiking' FVIII deficient plasma, from a severe haemophilia A donor, with Elocta-Sample S19.04 at a level similar to a patient trough level and Sample S19:05 at a level similar to a patient post treatment level.Participants were invited to perform a FVIII assay on each of the four samples using testing methods in regular routine use in their laboratory.Results: Result data was collected from 78 centres for a FVIII assay on all samples, with 56 centres performing a 1-stage FVIII assay and 22 centres performing a Chromogenic FVIII assay.9 participating centres performed both a 1-stage and a Chromogenic FVIII assay.1-stage FVIII: • S19:02 Median results IU/dL = 2.4; Range = 0.82-5 IU/dL CV = 31.1% • S19:03 Median results IU/dL = 56.9;Range = 41.5-77IU/dL, CV = 15% • S19:04 Median results IU/dL = 5.3; Range = 3.16-7 IU/dL, CV = 19.2%• S19:05 Median results IU/dL = 55.7;Range = 40.2-78IU/dL, CV = 14.2%Chromogenic FVIII results: • S19:02 Median results IU/dL = 2.0; Range = 0.5-5 IU/ dL;CV = 58.7%• S19:03 Median results IU/dL = 66.9;Range = 53-103 IU/dL; CV = 14.5% • S19:04 Median results IU/dL = 5.0; Range = 1-11 IU/dL; CV = 36% • S19:05 Median results IU/dL = 71.0;Range = 55-107 IU/dL; CV = 14.8%Discussion/Conclusion: Careful interpretation of patient results is required.Result levels of ≤11 IU/dL for 1-stage FVIII assays were at most ~15% higher compared to chromogenic assays.At higher levels of Elocta, 55-70 IU/dL, Chromogenic assays were at most 20% higher compared to 1-stage FVIII assay results.There were no found differences between in-vitro spiked samples and patient samples, indicating spiked samples to be commutable.